> Using USB power!
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Mint_Sauce |
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Class : Apprenti
Posts : 9
Registered on : 10/10/2007
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Firstly, Freetrack looks great, thanks for making it!!
Secondly,
I bought the recommended wide angle IR leds, the ones mentioned in the PDF file. Now, I have the leds but what resistor (if any) do I need to use if I'm going to power them from the USB on my PC?
If I'm unable to use the USB, I can use the square 9v batteries which I have. I tried using the calculator but to be honest i'm not too hot on what's what so no idea what i'm supposed to be using. heh.
Thanks for any help, I'd love to get this soldered together and give it a go.  |
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Mint_Sauce |
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Class : Apprenti
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Registered on : 10/10/2007
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forgot to mention i'm using 4 x IR leds.  |
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frogger |
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Class : Apprenti
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Registered on : 10/10/2007
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usb gives u a power supply of 5v.
i have a 3 point cap running from 6v, the led's r 1.5v i dont use any resistors.
if u have spare led's u could try to run them from the 5v usb most of the time if the voltage is to high the led will be very dull but since they r iru would have to feel them, they would get very hot , although i would only try it if u have spares
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Mint_Sauce |
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Class : Apprenti
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ok, thanks. Do you run them in series or parallel?
so,
0 0 0 0
¦ ¦__¦ ¦__¦ ¦__¦ ¦
¦ ¦
+ -
or are all the led legs joined directly on the terminals?
Thanks!
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frogger |
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Class : Apprenti
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im not actualy sure , the leds r all the same way round and i just complete the current
ive just posted wat my cap it like if u want to see although it doesnt show the connections .
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tristan68 |
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Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
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Hello Mint Sauce, Frogger
Lets tell it once more :
LEDS ARE NOT LIGHT BULBS BUT DIODES
ITS THEREFORE DANGEROUS TO OPERATE THEM WITHOUT LIMITING RESISTOR DUE TO THEIR NON LINEAR VOLTAGE-CURRENT CHARACTERISTIC.
You can destroy your leds, or your motherboard (if you power them on USB) very easily.
There are few ways to operate leds directly on a voltage source, but you need to precisely know your components characteristics, so it's beyond most people knowledge and equipement.
So Frogger please don't spread such information, thanks.
@Mint Sauce :
You said in your first post you didn't understand the calculator. Can you please be more precise ? Thank you
Cya.
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Kestrel |
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Class : Webmaster (admin)
Posts : 780
Registered on : 13/07/2007
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******************************************************************
!!!!!!!!!!@@@@###**** USB WARNING ****###@@@@!!!!!!!!!!!!!
****************************************************************************
Don't stuff around with USB power, it can kill your motherboard in a heartbeat.
If you really want to use it, make sure you use a correctly rated PTC fuse (0.2A trip) and a good, safe, tested circuit with no possibility of short-circuit.
Edited by Kestrel on 10/10/2007 at 16h04. |
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tristan68 |
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Class : Electronicien en chef
Posts : 651
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lol hello kestrel
didn't take long to have an answer on this one  |
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frogger |
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Class : Apprenti
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damn my bad sorry guys 
i wasnt thinking about motherboard damage.
ive found power boxes to be safe would u recomend them ? |
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Mint_Sauce |
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Class : Apprenti
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woah! Thanks, I'll stick with a plug in multi thing. The power packs where you can select the voltage and rig it up to that. Would that be ok?
I'm using the recommended IR leds:
SFH485P
1.5 V 100(mA) 880 (nm) 5mm
I can use one of those square 9v batteries or teh plug in adapter. I'd prefer to use the plugin adapter as then I wouldn't have to worry about changing batteries etc.
What would my final circuit look like with what resistors?
Sorry, I used teh calculator but to be honest i'm a total beginner at electronics. I'm fine soldering etc but the amps and ohms stuff goes over my head. Thanks.
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tristan68 |
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Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
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Hello Frogger
Yes power boxes are good.
But as I said earlier, its dangerous to directly power leds on a power supply , without resistors (even on a power box).
Chances that'll work correctly are small, you'll most often :
- or underpower your leds (dim lighting) if your powerbox is too weak, or has a too low voltage
- or overpower them (less lifetime or even rapid destruction) very easily if your powerbox has eough voltage and power.
Thats due to the fact leds are not (like light bulbs) voltage driven , but current driven.
You can connect directly leds to a calibrated current generator (thats really ok), but such devices are difficult to find in shops.
So the most easy way to convert your voltage generator (power adapter or battery pack) in a "like current generator" is to add a limiting resistor in your circuit.
cya
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tristan68 |
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Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
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Hello mint sauce.
No need to worry, its ok , we re here to help
To use the wizard , you need to know 3 values :
Power supply voltage
Led forward voltage
Led forward current
lets imagine we use a 9v battery or a 9v power adapter and 4 x SFH485P leds
you have these values :
Power Voltage : 9v (adapter or battery dependent)
Led voltage : 1.5v (Led dependent)
Led current : 100 mA (Led dependent)
If you feed those 3 values in the led wizard , you'll get the following informations :
Diagram type : serial (all elements are wired one after the other)
resistor value (e12 range , thats ok) : 33 Ohms
since the power in the resistor is 0.27w, you'll need a resistor at least 0.5w (0.25w would be too small)
So , you go to your local electronics shop and ask for a : 33 ohms 5% 1/2w or more resistor
thats all
I'm avail for further questions.
Cya |
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Mint_Sauce |
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Class : Apprenti
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aah, great - thanks! I will go and have a hunt about for them! Thanks |
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Mint_Sauce |
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Class : Apprenti
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I've been trying to find the 33 ohm resistor I need to order but these big online places when you type 33 ohm resistor come up with about 3000 results... Is there a specific part number like the leds have that I can tap in to find these easier?
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tristan68 |
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Class : Electronicien en chef
Posts : 651
Registered on : 10/07/2007
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Hello Mint_Sauce
Resistors are rather common components , so you have plenty of variations.
Just stick to the values , and its ok :
33 ohms 5%
0.5w minimal (can be more)
then go for the cheapest 
usually , thats a carbon resistor...... |